18 replies to this topic

[rajenkins]

I was trying to go through all possible things that could cause the ECU to act as if there were more airflow than actually present.

 

The only bit left to consider was the brand new (and very expensive) EGR valve. If that was indicating it was open, it could cause the ECU to give more fuel to match the added air.

 

I swapped the motor unit on the top for the one off the old valve - and it now starts and ticks over without ann throttle. Fault valve unit.

 

I disconnected the battery for an hour to clear the settings from when it was messed up, then reconnected it and took it for a drive to try and let it set itself up.

 

 

It is still hunting / surging badly, especially with light throttle in traffic; a couple of times it just about gave me whiplash...

 

When stopping at traffic lights etc., it hunts between around 500 - 1100 revs for a while then settles at about 800-900 or so. It sometimes starts hunting again on its own.

 

I'm presently waiting for it to cool down enough to check the plugs again, to get an idea of the mixture.

[FRANZ]

Is there a split breather hose under the coil pack by any chance? The purge valve hose is there.

[FRANZ]

Symptoms of a Faulty Throttle Position Sensor

• An unexplainable bucking and jerking in the vehicle.
• Sudden idle surges.
• Sudden engine stalling without any apparent reason.
• Hesitation while accelerating.
• Sudden surges in speed while driving on the highway.
• Intermittently flashing of check engine light for no apparent reason.........

I don't know if this will work. If you start the engine and then disconnect the plug from the side of the throttle body on the throttle position sensor and open the throttle valve by hand at the throttle body you are letting more air into the manifold. Worth a try just to see what happens.

[rajenkins]

I forgot to say I've already tried the throttle position sensor, I had a spare from the previous Mondeo - it turned out to be the coil pack on that one.

[rajenkins]

I had left the battery disconnected overnight reset the ECU again..

 

It is still hunting/surging like crazy, whether at tickover or holding the throttle so the revs are around 2000-2500.

 

Watching diagnostics at the same time, the throttle position sensor output is rock solid stable at tickover and when the accelerator is held still at higher revs.

 

At tickover, while its hunting, revs are between about 700-1300, MAP output is varying between around 15-40 KPa. 

Short term fuel trim around +27 to +33%, long term trim zero.

Oxygen sensor 1 anything from near zero to 0.9V, average about 0.35

 

The inlet temperature reading is around 20'C, the present ambient temperature.

 

 

I've just tried short blasts of liquid propane (from a pound shop "canned air" aerosol) all around the inlet manifold, underneath near the oil separator and around the pipes and valves at the right of the engine where the pipes go to the solenoid and brake servo, again with no effect at all.

 

Removing the oil filler cap has no effect at all (other than mess), which I think rules out the PCV valve leaking.

 

 

The spark plugs are no longer sooted up, which is a massive change from when it had the faulty EGR valve on it.

 

 

Any ideas, anyone?

[FRANZ]

What happened with my car is that because there is high vacuum in the inlet manifold at idle a split in the PCV valve hose was opening slightly and drawing in air and when the car was on the road the vacuum was more equal to atmospheric pressure so the split was not drawing in air. I know you have checked many things and I also sprayed engine start in the inlet manifold area which made no difference when I did it. I wonder if the sealing grommet on your PCV valve is okay? Hope you find out what is wrong with it soon. If the PCV valve does not regulate air flow the engine will act like it had a vacuum leak.

[rajenkins]

Solved!

 

The very last possible sensor I could see was the knock sensor below the manifold. I managed to get it out with the manifold in place it tested fine on an oscilloscope, but there was just no way I could get the bolt to start in the thread when trying to refit it.

 

I had to take the manifold off again, but that game me a chance to double check everything. It was all connected properly and the new PCV breather hose (16mm fuel pipe, as advised by another user) was still in the correct place on the fittings, nothing had moved.

 

While putting it back together I realised there was one part that was unproven - the new TMAP sensor, which was the same brand as the faulty new EGR  valve.

 

 

I refitted the original TMAP sensor, which was replaced to try and solve the hunting caused by the faulty EGR valve.

 

It started first time, smooth tickover, no jerking or hunting when idle etc...

 

 

It's either a million to one fluke or there are some counterfeit (or re-labelled reject) parts getting through to a major distributor. 

 

(The faulty EGR valve motor literally runs backwards - it moves to fully open when it should be fully closed. The motor base plate is not welded on the plastic pins, as the original one is; it fell apart while I was examining it, after the pushrod wound out so far it came clear of the motor base).

[FRANZ]

I got a TMAP sensor from China when I did the PCV hose replacement and the engine management light came on. Eventually refitted the original one which was not faulty as I learned and the the engine management light went out. Good result getting your car fixed.

[mondeo df]

Well done to you and to everybody that contributed. I've learned a lot from reading of your woes!